Gear Hanger / small bolt help required

[Fatal Swan]

The bike I bought (2005 Principia Ellipse) had, or quickly developed, a missing M3 hanger bolt and after replacing it I found that the bolt wouldn't tighten, I assume since the tiny thread was damaged. Fortunately the damaged thread was teh one on the hanger and not the frame so off I went to gearmechhanger.com for a £27 (!) replacement:

Tightening up the same bolt (the bottom one in the photo below) with little torque - i.e. using the long end of a tiny allen key - immediately stripped the hanger thread. The company are sending me a replacement but clearly this is an issue in the hanger design - the thin aluminium back plate which the screw threads into can't be more than a couple of mm thick, maybe with 2-3 turns of thread at most.

So the question is, how can I stop it happening again? I don't know how sensible it is to use blue threadlock with such small headed bolts - I guess they could easily get mashed trying to remove them. I don't know if the metals are suitable for threadlock (the bolts are steel, the hanger aluminium), or whether I could even torque the bolt up enough for it to be effective? One idea I had is to buy a longer bolt for the hanger, say with an extra 5mm on the end that would stick through the back, and then attach a steel M3 nut against the back plate, to take some of the burden off the tiny aluminium thread of the hanger. But I have no idea if that would work?

But now I think of it, I guess I could have just used a longer bolt and a nut on the back even on the old hanger with the stripped thread (and saved myself the £27!)...

Any advice please?

 

[joss]

Re:

If you are concerned about using threadlock products you can use 'boiled linseed oil' it goes very tacky as it dries and we used to use it for locking spokes, it is far easier to undo any screws etc.

 

[hamster]

2 or 3 threads is clearly inadequate so it is a lousy design.

You cannot put a nut on the inside edge I suspect as it will likely foul the cassette lockring. It could be possible to bolt the other way - countersink the inside edge and then fit a washer and nut on the outside of the frame. However I don't think you need worry too much about strength as the hanger will be securely held in place by the QR of the rear axle.